Lec.5
Cavity Preparation
‫جابر االبراهيمي‬.‫د‬
Mechanical alteration of a tooth to receive a restorative material which will
return the tooth and area to proper form, function, and esthetics Preparation
procedure includes all defective and friable tooth structure. The carious material
is removed and the cavity is given a form that will assure –proper retention for the
restorative material, -adequate resistance to fracture during function, -immunity
from recurrence of caries at the margins of the restoration -and protection for the
vital pulp Areas of Liability to Caries.
Pits and Fissures:
These are enamel defects or faults, which result from incomplete union of enamel
lobes during formation of enamel. They are actual openings in which we can
force an explorer or a probe and upon withdrawal, the explorer is met with
resistance, food debris stagnates in these areas.
Fissure results from
the incomplete union of two enamel lobes during the
formative period of enamel. If complete union occurs between two enamel lobes,
the result will be a groove. The explorer in this case will pass smoothly because
there is no defect in the enamel.
A pit results from the incomplete union of three enamel lobes during its
formation, if complete union happens, the result will be a fossa
Smooth Surface area: a-Areas in the proximal surfaces of teeth gingival to the
contact area.
Contact area: Areas between two adjoining teeth is a place where food debris
can stagnate and ferment the acid produced will decalcify enamel, where
interproximal cavities occur.
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Walls and Angle of Cavities: Black gave the following rules for naming the
internal parts of cavities.
Rule I : The walls take the names of the adjacent tooth surfaces.
Rule II: That wall of a prepared cavity, which is occlusal to the pulp, and in a
plane at right angles to the long axis of the tooth, is called the pulpal wall or floor.
In case the pulp of the tooth is removed, and the cavity thus extended to include
the pulp chamber; that wall is called the sub-pulpal wall.
Rule III: The wall which is parallel to the long axis of the tooth and
approximates the pulp, is called the axial wall.
Rule IV: All the line angles are formed by the junction of two walls along a line,
and are named by combining the names of the walls joining to form the angle.
Rule V: All point angles are formed by the junction of three walls at a point, and
are named by joining the names of the walls forming the angle.
The Cavo-surface Angle: Is the angle formed by the junction of the
wall of
the cavity with the surface of the tooth. The cavo-surface angle of a cavity will
be of enamel, while in cavities present in the root of teeth, which are exposed due
to gingival recession, the cavo- surface angle will be cementum. The enamel
margin includes the whole outline of the prepared cavity.
The Dentino-Enamel Junction: Also called amelo- dental junction, is the line
of junction of dentin and enamel as it appears in the walls of the prepared
cavities. The Enamel Wall: Is that portion of a prepared cavity, which consists
of enamel, It includes the thickness of the enamel from the dentino-enamel
junction to the cavo-surface angle.
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The Dentin wall: that portion of the wall of a prepared cavity, which
consists of dentin.
Pulpal Wall: The wall of the prepared cavity which is occlusal to the
pulp and in a horizontal plane at right angle to the long axis of the
tooth.
Axial Wall: Any wall in the prepared cavity, which is parallel to the
long axis of the tooth.
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Dental caries
Dental caries is an irreversible microbial disease of the calcified tissues
of the teeth, characterized by demineralization of the inorganic portion
and destruction of the organic substance of the tooth, which often leads to
cavitation.
Pathway of dental caries.
Enamel:
First component of enamel to be involved in carious process is
the
interprismatic substance. The disintegrating chemicals will proceed via
the interprismatic substance, causing the enamel prism to be undermined.
The resultant caries involvement in enamel will have cone shape. In
concave surface (pit and fissures) base towards DEJ. In convex surfaces
(smooth surface) base away from DEJ.
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Dentine:
First component to
be
involved
in
dentin is
Protoplasmic extension within the dentinal tubules. These protoplasmic extensions
have their maximum space at the DEJ, but as they approach the pulp chamber and
root canal walls, the tubules become more densely arrange with fewer
interconnections.
■ So caries cone in dentin will have their base towards DEJ. Decay starts in
enamel then it involves the dentin. Wherever the caries cone in enamel is larger or
at least the size as that of dentin, it is called forward decay (pit decay). However
the carious process in dentin progresses much faster than in enamel so the cone in
dentin tends to spread laterally creating undermined enamel. In addition decay can
attack enamel from its dentinal side. At this stage it becomes backward decay.
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Classification of dental caries according to anatomical sites
1. Pit and fissure caries (OCCLUSAL CARIES)
 Pit and fissure caries of the primary type develops in the occlusal surface
of molar and premolar, in the buccal and lingual surface of the molar and
in the palatal surface of the maxillary incisors.
 Shape, morphological variation and depth of pit and fissures contribute
to their high susceptibility to caries.
 Enamel in the extreme depth is very thin or occasionally absent and thus
allows the exposure of dentin.
 Pit and fissures affected by early caries may appear brown or black and
will feel slightly soft and ‘catch’ a fine explorer point. Entry site may
appear much smaller than actual lesion, making clinical diagnosis
difficult.
 Carious lesion of pits and fissures develop from attack on their walls. In
cross section, the gross appearance of pit and fissure lesion is inverted V
with a narrow entrance and a progressively wider area of involvement
closer to the DEJ.
2. Smooth surface caries
 Less favorable site for plaque attachment, usually attaches on the
smooth surface that are near the gingiva or are under proximal contact.
 In very young patients the gingival papilla completely fills the
interproximal space under a proximal contact and is termed as col.
Also crevicular spaces in them are less favorable habitats for s.mutans.
 Consequently proximal caries is less lightly to develop where this
favorable soft tissue architecture exists.
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3. Linear enamel caries
 Linear enamel caries ( odontoclasia ) is seen to occur in the region of the
neonatal line of the maxillary anterior teeth.
 The line, which represents a metabolic defect such as hypocalcemia or trauma of
birth, may predispose to caries, leading to gross destruction of the labial surface
of the teeth.
 Morphological aspects of this type of caries are atypical and results in gross
destruction of the labial surfaces incisor teeth.
4. ROOT SURFACE CARIES
 The proximal root surface, particularly near the cervical line, often is unaffected
by the action of hygiene procedures, such as flossing, because it may have
concave anatomic surface contours (fluting) and occasional roughness at the
termination of the enamel.
 These conditions, when coupled with exposure to the oral environment (as a
result of gingival recession), favor the formation of mature, caries-producing
plaque and proximal root-surface caries.
 Root-surface caries is more common in older patients.
 Caries originating on the root is alarming because
1. It has a comparatively rapid progression
2. It is often asymptomatic
3. It is closer to the pulp
4. It is more difficult to restore
 The root surface is refer the enamel and readily allows plaque formation in the
absence of good oral hygiene.
 The cementum covering the root surface is extremely thin and provides little
resistance to caries attack.
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 Root caries lesions have less well-defined margins, tend to be U-shaped in
cross sections, and progress more rapidly because of the lack of protection from
and enamel covering.
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